The hepatitis C virus (HCV) is a single-stranded 9.4 Kb RNA virus recognized as the responsible agent for certain non-A, non-B forms of hepatitis. The viral genome of HCV codes for a polyprotein with approximately 3010 amino acids which, after translation, undergoes several maturing stages, leading to production of so-called structural proteins and of so-called non-structural (NS) proteins. The structural proteins of the HCV virus are the nucleocapsid proteins (corresponding to the C region of the HCV genome), the matrix protein (M), and two glycosylated envelope peptides, gp33 (E1) and gp72 (E2/NS1). The non-structural proteins are NS2 which is a protein bound to the viral membrane, NS3 which plays the roles of protease and helicase, and NS5 which corresponds to viral polymerase. The function of NS4 is still unknown. Clinical studies have shown that antibodies specifically directed against the preserved regions of the nucleocapsid and against NS3 appear early after HCV infection. Hence these two proteins are excellent markers for diagnostic tests of HCV infection. Other studies have shown the existence of several immunodominant antigens, particularly the C33 antigen of the NS3 region and more particularly the antigen noted C33c corresponding to a fraction of C33 (see WO 9115771). However, obtaining these peptides, one of which has 266, and the other, 93 amino acids in an isolated form by genetic recombination or chemical synthesis presents a number of obstacles linked in particular to post-translational modifications that are necessary for obtaining sufficiently immunoreactive peptides, or to difficulties involved in chemical synthesis of peptides of such length.
Surprisingly, the discovery has been made of a polypeptide synthesized chemically, or by genetic recombination methods, which has undergone no modification after its synthesis, which is capable of being recognized by antibodies specific to HCV infections, notably anti-HCV, while its sequence has no analogy with that of the C33 protein.